Yes, BOSS is safe as long as they have grit to grind it up in their gizzard and you do not overdo it.
I cannot come up with a link to that specific bag of Great Value BOSS to see if it gives an analysis of nutrients. Boss is typically fairly high in protein and oil. The oil is where you don't want to feed them too much. They need a certain amount of fats and oils for healthy body function but too much can cause some issues. So limit how much you give them.
Some breeders that show chickens feed them a small amount of BOSS. The oil in BOSS helps make the feathers shiny. It doesn't take much, just a few seeds will do. I do not feed them myself so I don't know a safe amount but I'd think two or three tablespoons per bird would be more than enough.